1、
2、ScheduledThreadPoolExecutor和Timer类似，可以设定一段时间delay之后或者按照一定的rate来执行任务。
3、ScheduledThreadPoolExecutor继承自ThreadPoolExecutor，但是ThreadPoolExecutor的一些API对ScheduledThreadPoolExecutor是无效的，因为ScheduledThreadPoolExecutor本质上是一个只有coreSize大小的而且BlockingQueue为inbound的一个线程池。
a few of the inherited tuning methods are not useful for it. In particular, because it acts as a fixed-sized pool using corePoolSize threads and an unbounded queue, adjustments tomaximumPoolSize have no useful effect. Additionally, it is almost never a good idea to set corePoolSize to zero or use allowCoreThreadTimeOut because this may leave the pool without threads to handle tasks once they become eligible to run.